When I did mine (on the TJ), I jack it up against the body, center punched it, then dropped it, drilled, did the inserts, cleaned the paint, test fitted, RTV'd the back of the slider, jacked it up in place, aligned, then screwed that thing to the tub. I forget how they mounted under the tub, think to the body mounts. Ran a bead of RTV along the top, smoothed with a spoon, and forgot they were there. I didn't have gaskets on the backside, but that would have been a good idea.
Anyway, along with what Kev said, RTV the holes with some black RTV and you'll be golden.